The invention relates to an imaging spectrometer, particularly for use in endoscopes, surgical microscopes and colposcopes for the diagnostic examination of body tissue.
In known endoscopes, white light is connected via a fiber optic system to body cavities, where the light shining in is then reflected, dispersed and absorbed. The reflected and dispersed portion of the light is focussed on a fiber optic image transmitter. The image transmitter usually consists of several thousand individual fibers, which transmit a coherent image from the body. This image is then projected for an observer (e.g., the treating physician) via an endoscopic eyepiece. Alternatively, instead of the eyepiece, a color image camera can be used, so that the reflection images (with negligible dispersion) can be depicted for the observer on a color screen. Using the known endoscopes and imaging techniques describes above; it is possible to diagnose large invasive tumors easily and relatively reliably. However, early, superficial non-invasive carcinomas often remain undetected.
WO A 90/10219 and WO A 86/02730, each show an endoscopic imaging system for tumor diagnosis. The light of a fiber bundle is split into four beam paths. In each beam path, a different color filter is arranged. Behind the color filters, the beam paths are imaged on a intensive CCD camera. The digital image is shown on a screen, which detects an incorrect color image.
All of the systems described provide only a spectrogram without any image information or, at the most, four spectral image data. The use of prisms or color filters requires equal beam paths for imaging the proportional color data. Currently, due to unsolved technical problems with multiple reflections of prisms, no arrangement that produces more than four partial images by means of beam dividers is technically feasible. To reliably diagnose tumors on the basis of image information, however, at least 16- or, preferably 32-spectrally-different partial images that can be simultaneously superimposed are required.
U.S. Pat. No. 4,678,332 discloses an apparatus for the isochronous analysis of the spectrum of an object, wherein the radiation of an object is connected by means of a collector optical system to a fiber optic cross-sectional converter. The virtually linear output radiation is imaged by means of a collimator optical system on a diffraction grating, and then spectrally decomposed and imaged via a further optical system on a matrix-type optical detector.
Photochemistry and Photobiology, 1996, 63(5), 608-614 describes an imaging spectrometer wherein interference phenomena during the superimposition of light waves for measurement and observation purposes can be analyzed by means of a Sagnac interferometer. With the help of a scanning process, an interferogram is imaged on a CCD chip. A subsequent Fourier transformation then yields a spectrum on each pixel. Image collection using this procedure takes about 50 seconds. This is followed by an image processing time of 2 to 4 minutes. The images obtained contain 10 to 30 spectral data per image pixel and are well suited for distinguishing between objects with only slight spectral differences. However, the relative slowness of the image processing limits the use of this device to microscopic measurements and to finding objects that are moving slowly or hardly at all. The process and device are therefore unsuitable for clinical imaging. In addition, the optical and mechanical structures of the device are very complex and cost-intensive.
From DE 1996 16 176 A1, a device for recognizing properties of moved objects is known. The device has a detector arrangement equipped with a filter arrangement for recording and exposing images of objects in different wave length ranges; a storage device for storing the wave-length-dependent image point data; and an evaluation unit that, depending on preestablished wave length information on the object and on the wave-length-dependent pixel data, determines the properties of the object. Located between the object and detector arrangement are at least two wave-length-selective filters and, associated therewith, at least two image forming optical systems to project object images of different wavelengths onto different local areas of the detector arrangement. It is disadvantageous in the known device that the adjustment between local and spectral resolution must be preset. Particularly in the area of diagnostics, it is necessary to search a broad tissue region for changes. If suspect tissue is found, it is examined more closely. However, because up to 16 spectral data are needed for unambiguous diagnosis, there is a corresponding limit on local resolution, which in turn makes detection more difficult.